Fractalkine (FKN) is a transmembrane chemokine that is expressed on the surface of activated endothelial cells and binds to the CX3CR1 receptor. The binding of membrane-bound FKN to membrane-bound CX3CR1 mediates strong cell-cell adhesion without the involvement of selectins or integrins. Secreted FKN, which is shed from membrane-bound FKN, also binds to CX3CR1 and induces the activation of integrin and cell chemotaxis.
Expression of FKN is induced on the surface of endothelial cells by proinflammatory cytokines. The elevated expression of FKN and the accumulation of CX3CR1+ cytotoxic effector lymphocytes and macrophages have been reported in subjects with numerous disorders, including inflammatory and autoimmune disorders, including ulcerative colitis (UC), Crohn's disease (CD), rheumatoid arthritis (RA), autoimmune hepatitis (AIH), multiple sclerosis (MS), and diabetes mellitus. Umehara et al., Arterioscler. Thromb. Vasc. Biol. 24:34-40 (2004) describes the role of FKN in atherosclerosis and vascular injury. Nishimura et al., Ann. NY Acad. Sci. 1173:350-356 (2009) discusses FKN as a potential therapeutic target for inflammatory bowel disease such as UC and CD.
Antibodies and FKN-binding fragments of antibodies are desirable therapeutic agents because of their specificity. Antibodies and FKN-binding fragments may be used to target specific cells or tissues, thereby minimizing the potential side effects of non-specific targeting. There is a need to identify and characterize therapeutic antibodies useful in the treatment of inflammatory disorders, including those that are described herein.